1. Field of the Invention
This invention relates to the field of tensile strength members. More specifically, the invention comprises a rope or cable termination that includes an instrument package useful for things such as position monitoring and load monitoring, as well as other components that are connected to the instrument package.
2. Description of the Related Art
In this disclosure the terms “rope” and “cable” are used interchangeably. Both are examples of a “tensile strength member,” meaning a component that readily transmits tensile forces but not compressive forces. Tensile strength members must generally be connected to other components in order to be useful. A flexible cable provides a good example. Most cables include some type of end-fitting configured to transmit a load. For example, a cable used in a hoist generally includes a lifting hook on its free end. This lifting hook may be rigged to a load. The assembly of an end-fitting and the portion of the cable to which it is attached is commonly called a “termination.” Most high-strength cables are presently made of steel. The cable is a wound or braided assembly of individual steel wire. An end fitting (such as a lifting hook) is often attached to the steel cable by placing a length of the cable within a cavity running through a portion of the end fitting. The wires within the end fitting are splayed apart and a potting compound is then used to lock the wires within the fitting. The term “potting compound” means any substance which transitions from a liquid to a solid over time. Examples include molten lead, thermoplastics, and UV-cure or thermoset resins (such as two-part polyesters or epoxies). Other examples include plasters, ceramics, and cements. The term “solid” is by no means limited to an ordered crystalline structure such as found in most metals. In the context of this invention, the term “solid” means a state in which the material does not flow significantly under the influence of gravity. Thus, a soft but stable wax is yet another example of such a solid.
Molten lead was traditionally used as a potting compound for steel cables. Once the individual wires were splayed within the expanding cavity of an end-fitting, molten lead was poured into the cavity. The lead then solidified and locked a portion of the cable in the cavity. In more recent years lead has been replaced by high-strength epoxies.
Modern cables may still be made of steel, but high-strength synthetic filaments are becoming more common. These include DYNEEMA, SPECTRA, TECHNORA, TWARON, KEVLAR, VECTRAN, PBO, carbon fiber, and glass fiber (among many others). Modern cables may also be made of older, lower-strength synthetic materials such as NYLON. In the case of high-strength synthetics, the individual filaments have a thickness that is less than that of human hair. The filaments are very strong in tension, but they are not very rigid. They also tend to have low surface friction. These facts make such synthetic filaments difficult to handle during the process of adding a termination and difficult to organize. Hybrid cable designs are also emerging in which traditional materials are combined with high-strength synthetic materials. These present additional challenges, since the metal portions may be quite stiff while the synthetic portions will not be.
Those skilled in the art will know that cables made from synthetic filaments have a wide variety of constructions. In many cases a protective jacket will be provided over the exterior of the synthetic filament. This jacket does not carry any significant tensile load and it may therefore be made of a different material.
Most larger cables are made as an organized grouping of smaller cables. The smaller cables are often referred to as “strands.” One example is a parallel core of synthetic filaments surrounded by a jacket of braided filaments. In other cases the cable may be braided throughout. In still other examples the cable construction may be: (1) an entirely parallel construction enclosed in a jacket made of different material, (2) a helical “twist” construction, (3) a more complex construction of multiple helices, multiple braids, or some combination of helices and braids, or (4) a hybrid construction including metallic constituents.
The reader is referred to commonly-owned U.S. Pat. No. 8,371,015 for more detailed descriptions regarding the application of an attachment to a sub-component of a larger cable. The '015 patent explains how individual anchors can be attached to the strands and the anchors can then be attached to a common collector to create a uniform load-bearing structure.
The present invention is not limited to multi-stranded terminations. Any form of cable termination may be used, such as a single socket for example. The exemplary embodiments depicted all include multi-stranded terminations but this fact should not be viewed as limiting. The embodiments also pertain to the specific field of deep water lifting and lowering. The invention is by no means limited to this field, however. Finally, the termination types depicted are most suitable for high-strength synthetic fibers. The present invention may be applied to many different cable types and is not limited to such fibers.